1. Field of the Invention
The present invention relates generally to stents, stent-grafts, and other endoluminal prostheses for use in blood vessels and other body lumens. In particular, the present invention provides an endoluminal prosthesis frame which is highly compressible for deployment from a small delivery catheter, and which provides enhanced structural support when expanded in the body lumen.
The use of stents and other endoluminal prostheses is often indicated when there is a desire to maintain patency of a body lumen. Stents have commonly been used in blood vessels, the ureter, and the biliary duct to treat luminal obstructions and/or weakness. Of particular interest to the present invention, vascular stents have demonstrated significant success in inhibiting restenosis following angioplasty and other primary interventional treatments in the vasculature. Lined stents, often referred to as vascular stent-grafts, hold great promise for the reinforcement of blood vessels for the treatment of aneurysms, for lining blood vessels for the treatment of occlusive disease, and other conditions. In the case of aneurysms, the stent acts as a scaffold or framework for supporting a liner within the blood vessel to define an artificial blood vessel lumen. In the case of occlusive disease, the stent maintains luminal patency while the liner inhibits cellular intrusion into the lumen.
Vascular stents are typically delivered in a radially reduced or constrained configuration, and are expanded in situ at the target site. The stents may be plastically deformable and mechanically expanded at the target site, typically using a balloon catheter. Alternatively, the stents may be formed from a resilient material and released to self-expand at the target site. In a third general approach, the stents are formed from a shape-memory alloy and induced to expand at the target site by exposure to a temperature change. Regardless, the stent will usually comprise a network or lattice of structural elements which accommodates radial expansion from a small profile configuration (suitable for introduction and positioning of the prosthesis within the blood vessel), to a large profile configuration (in which the tubular prosthesis engages and supports the surrounding vascular wall). One common geometry for these stent frames comprises a plurality of diamond-shaped elements which are joined in a ring. These diamond-shaped elements are circumferentially expandable as the prosthesis is deployed from the small profile configuration to the large profile configuration. Other common geometries include helically wound wires and filaments, zig-zag rings, braided filaments, woven helical filaments and the like.
One disadvantageous characteristic that many prosthetic frame structures have in common is an axial length/diameter coupling effect: the axial length of at least some of the frame elements tends to decrease as the frame expands radially during deployment. With some frame structures, this coupling can lead to challenges in selecting the proper prosthesis size, and in positioning of the prosthesis during deployment. Fortunately, the overall axial variability of other frame structures is significantly less (so as to allow accurate positioning of the ends) while deployment of endoluminal prostheses for many applications does not require that the exact overall prosthetic length be known prior to deployment. These endoluminal therapies are gaining acceptance for use in treatment of diseased body lumens.
To still further enhance the efficacy of these endoluminal therapies and reduce the trauma to the patient, it is generally desirable to minimize the size (and specifically the cross-sectional dimensions) of the delivery system and prosthesis prior to deployment. For the prosthesis to effectively treat a diseased body lumen, it should have sufficient structural integrity and strength. These factors are generally enhanced by increasing the size of the structural elements of the expandable frame or stent. The structural design challenges can be particularly problematic when the frame comprises a resilient structure which is tightly compressed within a deployment catheter. The competing factors often dictate that a larger than ideal delivery system be used for many endoluminal therapies, which may make accessing the diseased region difficult, traumatic, and/or impossible.
In light of the above, it would generally be desirable to provide improved endoluminal prosthetic structures, methods, and delivery systems. In particular, it would be beneficial to provide improved prosthetic frames having the desired structural strength and integrity, but with a reduced overall delivery system profile. It would be best if these improvements could be provided using existing stent production in prosthetic assembly in deployment techniques to further enhance the applicability of these therapies.
2. Description of the Background Art
Exemplary methods for making stents are described in published PCT Application WO 97/27959, having a priority date of Jan. 30, 1996, and European Patent Application No. 97906450.8, filed Jan. 29, 1997, the full disclosures of which are incorporated herein by reference. An exemplary delivery device for endoluminal prostheses is described in Provisional U.S. Application Serial No. 60/102,562, filed on Sep. 30, 1998, the full disclosure of which is also incorporated herein by reference.
U.S. Pat. No. 5,676,696 describes modular bifurcated intraluminal grafts and methods for their delivery and assembly. U.S. Pat. No. 5,716,365 describes a bifurcated endoluminal prosthesis, while U.S. Pat. No. 5,716,393 describes a stent with an end of greater diameter than its body. U.S. Pat. No. 5,766,237 describes a method for reinforcing a body vessel using an intraluminal stent.
Present invention provides improved endoluminal prostheses, prosthetic systems, and methods for preparation and use of endoluminal prostheses for treatment of diseased body lumens. The invention generally provides endoluminal prosthetic frame structures having circumferentially interspersed large and small expansible elements. These expansible elements, which are typically diamond-shaped, will often decrease in length as the tubular frame expands radially, although the overall length of the prosthetic frame and prosthesis will remain substantially constant. The prosthesis will often include a tubular liner supported by an axial series of ring frames having alternating large and small diamond elements, and can be loaded in a delivery catheter with the axial apices of the large diamond-shaped elements aligned with a small diamond-shaped element of an adjacent frame ring. To maintain adequate column strength, the adjacent ring frames may be attached to the liner so that the ring frames rotate relative to each other during expansion. As a result, the large diamond-shaped elements of adjacent ring frames can be aligned together once the prosthesis is expanded in the body lumen. This enhances the structural integrity of the prosthesis, particularly the expanded prosthetic column strength.
Work in connection with the present invention has shown that the frames of resilient endoluminal prostheses often become jumbled, overlapping in a disordered manner when tightly compressed in a small delivery catheter. For example, as independent ring frames of diamond-shaped elements are compressed radially, the apices extending axially toward adjacent ring frames increase in length. As the apices of adjacent ring frames will preferably be in close proximity and/or in contact once the prosthesis is expanded in the body lumen (so as to provide adequate column strength) the enhanced axial length of the apices in the small profile configuration results in these structures interfering and/or overlapping radially when compressed. To overcome this disadvantageous interference, the present invention accommodates the increased axial length of these apices using interspersed and often circumferentially alternating diamond-shaped expansion elements. While these smaller elements do help the frame both expand radially and support the liner, they do not generally contact the apices of adjacent ring frames when expanded. These smaller elements act as spacers when the ring frames are radially compressed to help ensure that the apices of adjacent ring frames have room to expand axially without overlapping during compression.
In a first aspect, the present invention provides an endoluminal prosthesis comprising a tubular frame having a proximal end, a distal end, and an axis therebetween. The frame is radially expansible from a small diameter configuration to a large diameter configuration for deployment within a body lumen. The frame comprises a circumferentially oriented frame loop defining a plurality of short, axially-oriented apices. The frame further comprises a plurality of long, axially-oriented apices which extend axially beyond the short apices. The long apices are circumferentially interspersed with the short apices.
In another aspect, the invention provides an endoluminal prosthesis comprising a first frame loop defining axial and circumferential orientations. The first frame loop includes interspersed large and small expandable elements. The large elements are axially longer than the small elements. A second frame loop is aligned co-axially with the first frame loop. The second frame loop is circumferentially expandable and includes interspersed large and small expandable elements. The large expandable elements are larger than the small expandable elements. At least one of the large expandable elements of the first frame loop is axially aligned with one or more associated small expandable elements of the second frame loop when the first and second frame loops are in a small profile configuration. At least one of the large expandable elements of the first frame loop is axially aligned with an associated large expandable element of the second frame loop when the first and second frame loops are in a large profile configuration.
In yet another aspect, the invention provides a tubular prosthesis for deployment within a blood vessel. The prosthesis comprises a tubular liner defining axial and circumferential orientations. A first ring frame supports the liner, and has an axial end. The first ring frame includes interspersed large and small diamond-shaped elements, the large elements defining apices adjacent the end. A second ring frame supports the liner adjacent the axial end of the first ring frame. The second ring frame includes interspersed large and small diamond-shaped elements. The apices of the first ring frame are disposed circumferentially between the large diamond-shaped elements of the second ring frame when the prosthesis is in a small profile configuration for insertion into the blood vessel. The apices of the first ring frame are axially aligned with the large diamond-shaped elements of the second ring frame when the first and second ring frames are in a large profile configuration engaging the surrounding blood vessel. The first and second ring frames rotate axially relative to each other as the prosthesis expands.
In yet another aspect, the invention provides a method for preparing an endoluminal prosthesis for deployment. The method comprises affixing a first ring frame to a tubular liner. The first ring frame has circumferentially interspersed small and large expandable elements. The second ring frame is affixed to the tubular liner and axially adjacent the first ring frame, the second ring frame also having circumferentially interspersed small and large expandable elements. The prosthesis is loaded into a delivery catheter in a small configuration with the large expandable elements of the first ring frame circumferentially interspersed with the large expandable elements of the second ring frame.